Induction heating apparatus



Dec. 4, 1962 E. F. MCBRIEN INDUCTION HEATING APPARATUS Filed June 29, 1960 FIG. I

a II I V o v d 0 A A I II A II V H 4 u l. A H V m G H V m H H V v V w G I I A G I, G J V 4 V I .V F Al F F 3 A F J. II ,v L V v A1 E A E A E E V 2 2 1 v q A n, DD 3 A l D A A G L V C II c H A c F ,V B V 3 N v L A A A A A A D D A J J C H 8 2 FIG. 3

N mm R B we M F D m w E ATTORNEY Uite This invention pertains to the art of induction heating apparatus and more particularly to an induction heating coil assembly capable of producing variable temperature patterns to accommodate the requirements of workpieces of different types and shapes.

In order to obtain either a uniform or varying temperature pattern over the surface of a workpiece, it has usually been considered necessary to design a solenoid heating coil with a particular diameter and length and with a varying turn spacing. For example, if a varying heating pattern was to be achieved over the length of a workpiece of constant cross-section, or a constant heating pattern over the surface of a workpiece of varying cross-section, the pitch and/ or diameter of the coil was varied along its length to obtain the desired result. It was necessary usually to assume a solution, build a coil, and observe the resulting heating pattern. The desired pattern was obtained only after a number of successive coil modifications; and, in general, the resulting coil was not satisfactory for other loads. That is to say, each new workpiece required a new design of heating coil, and since no two types of workpieces are identical, a specific coil design was required for each job.

It is a primary object of this invention to provide an induction heating coil assembly of constant length and pitch capable of achieving any desired heating pattern in any number of different workpieces. In this manner, only a single coil assembly need be provided to accommodate the various heating requirements of diilerent workpiece rather than a separate coil of special design for each different workpiece as was required in the past.

In accordance with the invention, a heating coil is provided having a length great enough to accommodate the longest workpiece which is to be heated. The coil has a constant diameter and pitch along its length and is provided with a tap at every point where the load cross-section may change or the specified temperature may change for the expected types and sizes of workpieces. A second coil, called a control coil, is also constructed having the same number of taps as the heating coil. its length, diameter, number of turns and other particulars may be the same as, or dilferent from, the heating coil as convenience dictates. The corresponding taps on the two coils are then connected in parallel. When a voltage is applied to the two coils in parallel, the current will divide according to the ratio of the impedances of the individual coil sections. Consequently, the current in any short section of the heating coil may be varied by changing the impedance of the matching section of the control coil. This may be easily accomplished by inserting magnetically permeable material, such as powdered iron slugs, into the sections of the control coil where the impedance is to be raised or low resistivity conducting material where the impedance is to be lowered. A change in impedance can, of course, also be achieved by varying the cross-sectional area of the powdered iron slug or low resistivity conducting material disposed within the control coil, as the case may be. Once the dimensions and location of the inserts within the control coil are determined for a given workpiece, they can either by made into a long rod to be associated with the part, or the locations can be merely noted and the same inserts used for several parts. The control coil is not required to carry currents as large as in the tent O "ice heating coil. If 10% of the current is diverted to the control coil, the power in the load will be reduced to ap proximately of its former value. Assuming that the final temperature is proportional to the power, this will reduce the final load temperature, for example, from 2000 F. to 1600 F.

FIGURE 1 is an illustration of one embodiment of the invention wherein a varying heat pattern is produced on a workpiece or" constant cross-section by means of a control member of low resistivity material in the control coil;

FIGURE 2 is an illustration of another embodiment of the invention wherein the heating pattern of FIGURE 1 is again produced in a workpiece of constant cross-section, but in this case a control member of magnetically permeable material is employed in the control coil; and

FEGURE 3 is an illustration of another embodiment of the invention wherein a uniform heating pattern is produced over the surface of a workpiece of variable crosssection by means of a control member of low resistivity conducting material in the control coil.

Referring to FTGURE 1, there is shown a heating coil Til and a control coil 12 which, for purposes of explanation, has the same length, diameter and pitch as the heating coil itl. Both coils in and 12 are connected in parallel across a source of alternating current voltage 14, substantially as shown. Connected in shunt with source 14 is the usual power factor-correcting capacitor 16. The coil 16 has taps A through I which are connected to corresponding points A through I on the control coil 12. In this manner, each coil is divided into successive short sections which are connected in parallel.

Disposed within heating coil 10 is a workpiece lit, and within the control coil 12 is a control member 20 which may be of low electrical resistivity, or high electrical resistivity, or magnetically permeable material depending on the desired heat pattern in the workpiece 18. In FIG- URE 1, the control member 21 is of a low resistivity conducting material, such as copper. The workpiece 18 and control member 20 may remain stationary within their respective coils during a heating operation, or they may both be passed through the coil sections progressively as by means of hydraulic cylinders 22 and 24 which are connected to the ends of the workpiece and control member through fixtures 24 and 2d respectively.

It will be apparent that when a voltage is applied to the two coils, the current will divide according to the ratio of the impedances of the individual coil sections. Thus, between the left end of coil 12 and tap B, portion 23 of the control member 20 has a large cross-sectional area. Since it is of low resistivity conducting material, the im pedance in this section of coil 20 will be lowered so that a larger amount of the current will be diverted through control coil 12 between its left end and tap B, and the depth of heating produced in the workpiece between its left end and tap B will be relatively shallow. Between taps B and D, the cross-sectional area of the control member 29 decreases as at 30.

I Consequently, the impedance in the section of coil 12 between taps C and D increases so that a larger proportion of the current is diverted to the section of coil 10 between taps B and D to increase the depth of heating in this portion of the workpiece 18. Between taps D and F, however, the cross-sectional area of the control member 20 again increases as at 32 so that the depth of heating between taps D and F on coil 10 decreases. Between taps F and G, the cross-sectional area of the control member 20 is very small as at 34, so that the depth of heating between taps F and G on heating coil 10 again increases. Finally, between tap G and the right end of coil 12, the cross-sectional area of the low resistivity conducting material increases as at 35 to de crease the depth of heating on the workpiece between tap G and the right end of heating coil 10.

he control member 2t} need not, of course, be of the same material throughout, nor of the same diameter. Thus, the material between the left end of coil 12 and the tap B could be low resistivity material to decrease the impedance of that section; while that between taps B and D could be magnetically permeable material to increase the impedance of that section to a maximum and produce a maximum depth of heating between taps B and D on heating coil 10. Also high resistivity material can be used between certain taps which will produce a depth of heating between that of the low resistivity material and the magnetically permeable material. Upon consideration, it will be seen that a large number of combinations of low or high resistivity material and/ or magnetically permeable material in various diameters may be employed to obtain the desired heating pattern in the workpiece. Although the length, diameter and pitch of the control coil is the same as that of the heating coil for the embodiment shown in FIGURE 1, the pitch, diameter, length and other particulars of the control coil may be different, the only requirement being that the apparatus be designed to produce the correct impedances across the various sections of the control coil to effect the proper heating pattern in the workpiece 18. For that matter, the pitch of coil 12 may vary along its length just so long as the proper heating pattern is produced in the workpiece. Furthermore, control rnember 20 may be all in one piece as shown or may comprise separate iron or copper slugs, for example, which are positioned in the control coil 12 to achieve the desired heating pattern.

In FIGURE 2 another embodiment of the invention is shown which again includes the heating coil and the control coil 12, both of which are divided into sections connected in parallel. In this case, however, the control member 20 is of magnetically permeable material throughout so that its configuration is reversed with respect to the dummy load of FIGURE 1 which was formed of low resistivity conducting material. Thus, between the left end of coil 12 and tap B the diameter of the magnetically permeable material is reduced to decrease the impedance of the control coil between the left end and tap B whereby a larger portion of the current will be shunted through this section of the control coil, and a relatively shallow heating pattern will be achieved in the workpiece 18 between the left end of the heating coil and tap B. Between tap B and D on the control coil, the diameter of the magnetically permeable material increases so that the impedance of this section of the control coil increases to increase the depth of heating between taps B and D on the heating coil 10. Between taps D and F, the diameter of the magnetically permeable material of load 20 decreases to decrease the depth of heating in this section of the workpiece 18, and so on.

In FIGURE 3, another embodiment of the invention is shown which again includes the heating coil 10 and control coil 12. In this case, however, the workpiece has a variable cross-section along its length while the control member 20 is formed from low resistivity conducting material. It will be assumed that it is desired to produce a uniform heating pattern over the length of the workpiece 18. Consequently, between the left end of control coil 12 and tap A the diameter of the control member 20 is decreased to increase the impedance of that section. In this manner, the magnetic field between the left end of heating coil 10 and tap A will be increased to accommodate the reduced diameter section of the workpiece 18. Between taps A and D, the diameter of the control member increases to reduce the impedance of control coil between these taps and thereby decrease the strength of the magnetic field between taps A and D on heating coil 10. Consequently, although the diameter of the workpiece 18 increases between taps A and D, the depth of heating on its surface will be the same as that on the section between the left end of the coil and tap A due to the fact that a larger proportion of the current has been shunted through the control coil between taps A and D. Between taps E and H on the control coil, the diameter of the control member 20 again decreases to increase the impedance in the control coil between these points and divert a larger proportion of the current to the heating coil between taps D and H on the control coil. This will, of course, increase the strength of the magnetic field between the aforementioned taps on the control coil to produce the required depth of heating on the reduced diameter portion of the workpiece 18 between points D and H. As will be understood, since the diameter of the workpiece increases between taps H and I on the heating coil 10, the diameter of the control member also increases between taps H and I on the control coil 20. Similarly, the diameter of the workpiece and that of the control member decrease bet-ween taps I and I and the ends of the respective coils.

Obviously the control member 2% could be of magnetically permeable material rather than low resistivity conducting material in which case the shape of the control member 20 will be exactly opposite to that of the workpiece 18 to obtain a uniform heating pattern over the length of the workpiece.

The invention thus provides a means for achieving variable heating patterns in workpieces of different shapes and sizes within a coil of constant length, diameter and pitch. Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Having thus described my invention, I claim:

1. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section having a generally constant diameter and constant pitch throughout its length, a second induction coil section having a similar number of turns, taps spaced along the length of said first coil section, corresponding taps spaced along the length of the second coil section with the number of taps on the second coil section being equal to the number on the first coil section and the spacing between successive taps on the second coil section being proportional to the spacing between successive corresponding taps on the first coil section, means connecting each tap on the first section to its corresponding tap on the second section, means for connecting said first and second coil sections in parallel across a source of alternating current voltage, and a control member of magnetically permeable material having a variable diameter along its length disposed within said second coil section whereby the impedance presented between successive pairs of taps on the second coil section will vary to produce variable flux densities between successive pairs of taps on the first coil section.

2. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section having a generally constant diameter and constant pitch throughout its length, a second induction coil section having a like number of turns, taps spaced along the length of said first coil section, corresponding taps spaced along the length of the second coil section with the number of taps on the second coil section being equal to the number on the first section and the spacing between successive taps on the second coil section being proportional to the spacing between successive corresponding taps on the first coil section, means connecting each spam on tap on the first section to its corresponding tap on the second section, means for connecting said first and second coil sections in parallel across a source of alternating current voltage, and a control member of low resistivity conducting material having a variable diameter along its length disposed within said second coil section whereby the impedance presented between successive pairs of taps on the second coil section will vary to produce variable fiux densities between successive pairs of taps on the first coil section.

3. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section having a constant diameter and constant pitch throughout its length, a second induction coil section, separate portions on said first coil defined by taps spaced along the length of said first coil section, a corresponding number of separate portions on said second coil defined by taps spaced along the length of the second coil section, each tap on the first coil section connected to a corresponding tap on the second coil section, the separate portions of the first coil section connected in parallel with the corresponding separate portions of the second coil section, said first and second coil sections connected in parallel across a source of alternating current voltage, and core member in said second coil section for varying the reluctance presented to the magnetic field produced by the second coil section along its length whereby the impedance presented between successive taps on the second coil section will vary to produce variable magnetic fields between corresponding successive taps on the first coil section.

4. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section having a constant diameter and constant pitch throughout its length, a second induction coil section, separate portions of said first coil section connected in parallel with separate portions of said second coil section, said coil sections connected in parallel across a source of alternating current voltage and metallic members magnetically coupled with the portions of said second coil for varying the reluctance presented to the magnetic field produced by the second coil section along said portions of said second coil whereby the magnetic fields produced by the various portions of said first coil section will vary.

5. An induction coil arrangement adapted to produce a variable flux density pattern along the length of the workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, a second induction coil section, separate portions of said first coil section connected in parallel with separate portions of said second coil section, said coil sections connected in parallel across a source of alternating current voltage, and metallic members magnetically coupled with the portions of said second coil for varying the reluctance presented to the magnetic field produced by the second coil section along said portion of said second coil whereby the magnetic field produced by the various portions of said first coil section will vary.

6. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section having a constant diameter and constant pitch throughout its length, a second induction coil section having a constant diameter and constant pitch throughout its length, separate portions of said first coil section connected in parallel with separate portions of said second coil section, said coil sections connected in parallel across a source of alternating current voltage, and a control member having variable reluctance portions along its length and being disposed within said second coil section, said variable reluctance portions magnetically coupled with the separate portions on said second coil Whereby the impedance presented to successive portions of the second coil section will vary resulting in variable magnetic fields produced by successive portions of said first coil section.

7. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section having a constant diameter and constant pitch throughout its length, a second induction coil section, separate portions of said first coil section connected in parallel with separate portions of said second coil section, said coil sections connected in parallel across a source of alternating current voltage, control member having variable reluctance portions, said reluctance portions corresponding to the desired flux pattern and means for passing said workpiece through the first coil section while simultaneously passing said control member through the second coil section.

8. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, a control member, a second induction coil section adapted to receive said control member, said control member having a variable reluctance along its length, separate portions of said first coil section connected in parallel with separate portions of said second coil section, said coil sections connected in parallel across a source of alternating current voltage, and means for feeding said workpiece axially through said first coil section while simultaneously feeding the control member axially through said second coil section.

9. The combination claimed in claim 8 wherein the workpiece has a length equal to that of the control memher and wherein the control member and the workpiece are moved through their respective coil sections at equal speeds with the leading edges of the workpiece and control member entering the coil sections at the same time.

10. An induction coil arrangement adapted to produce a variable flux density pattern along the length of a workpiece comprising, in combination, a first induction coil section adapted to receive a workpiece to be heated, said first coil section being divided into a number of successive separate portions by a number of taps, adjacent taps connected to separate control coil portions, said control coil portions connected in parallel with said separate coil portions, said control coil portions and said first coil section connected in parallel with a source of alternating current voltage, and a metallic member magnetically coupled with said control coil portion to vary the reluctance of said control coil portions, said metallic member having diiferent reluctance portions magnetically coupled with difierent control coil portions.

11. The induction coil arrangement as defined in claim 10 wherein said workpiece is moved through the first coil and the metallic device is moved through the control portions in unison with said workpiece, said different reluctance portions causing separate portions on said first coil to heat the workpiece at the desired rate as a given portion of the workpiece passes said separate portion of the first coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,986,353 Northrup Jan. 1, 1935 2,383,992 Sherman Sept. 4, 1945 2,452,197 Kennedy Oct. 26, 1948 2,470,443 Mittelmann May 17, 1949 2,490,104 Strickland Dec. 6, 1949 

